The present invention relates generally to electrical circuit breaking devices and more particularly to a vacuum type circuit interrupter with separate current carrying and arcing electrode contact surfaces which are of predetermined configuration and which move relative to one another in a predetermined way for providing improved current carrying capabilities while, at the same time, maintaining reliable interruption capabilities.
Vacuum type circuit interrupters are usually called upon to carry a steady state current of several hundred to several thousand amperes. When a fault occurs, the contact must be rapidly separated to achieve the desired separation as soon as possible. Small electrodes have small mass and can be rapidly separated with reasonable forces. Unfortunately, small electrodes are limited in the steady state current they can carry without overheating. Larger diameter electrodes spread the point of contact (asperities), reduce the power dissipated at the contact interface and provide a further advantage of being able to interrupt larger fault currents. Unfortunately, large electrodes in general have greater mass and require greater forces to achieve the same separation at the same time or stated another way, when applying the same force, the more massive electrodes separate at a slower rate of speed, if at all.
As will be discussed in more detail hereinafter, the present invention combines the advantages of larger current carrying electrodes having a relatively large mass with the advantages of smaller arcing electrodes by providing a particular means for and method of separation between the separate current carrying and arcing contact surfaces. In this regard, reference is made to U.S. Pat. Nos. 3,211,866 (Crouch et al) and 3,283,100 (Frink). Each of these patents discloses a vacuum type circuit interrupter which includes current carrying contacts and separate arcing contacts. In each of these disclosures, one fixed electrode defining a fixed contact surface is provided on one side of the interrupter and two electrically connected movable electrodes, each having its own contact surface, are provided on the opposite side of the interrupter. During normal operation, the interrupter described in each of these patents passes current by maintaining each of its movable electrodes in either direct contact with the fixed electrode or indirectly in contact therewith. For example, in the Crouch et al patent, both of the movable electrodes are in direct contact with the fixed electrode, whereas in the Frink patent one of the movable electrodes is in direct contact with the fixed electrode while the other movable electrode is indirectly connected therewith by means of a slotted metallic cylinder and condensing shield. However, in each case, the circuit is opened by first separating one of the movable electrodes from the fixed electrode before separating the other movable electrode from the fixed electrode. From an operation standpoint, only the contact surfaces which are subsequently separated act as arcing contacts.
While each of the references just described discloses a vacuum type circuit interrupter including separate non-arcing and arcing contact surfaces, neither recognizes or remotely suggests combining the advantages of a large contact surface with a small contact surface for improving the current carrying capability of its interrupter while at the same time providing satisfactory current interruption. Moreover, neither of these interrupters by the very nature of their design is capable of taking advantage of such a combination. More specifically, in each of these prior art interrupters, the movement of each of the two movable contact surfaces is interlocked with the other such that predetermined movement of the first movable contact surface causes subsequent movement of the second movable contact surface. Moreover, the two surfaces move at the same speed and by means of a common application of force.
Applicants have found that to provide satisfactory separation of the larger current carrying contact surfaces and the smaller arcing contact surfaces, the electrodes should be moved by separate independent means. This provides three distinct advantages over the interlocked movement described in the Crouch et al and Frink patents. First, the smaller electrode can be more readily moved at a faster rate of speed than the larger electrode for quicker separation. Second, the application of force required to move the smaller electrode by independent means does not have to be the same as the force required to move the larger electrode and, hence, can be smaller in magnitude. Third, the timing between movement of the larger electrode and the smaller electrode can be easily adjusted and even changed significantly if necessary using independent moving means whereas it would not be as easy to do this with the interlocked means disclosed in the cited patents.